1. Field of the Invention
The invention relates to devices for measuring the volume of air inspired by patients as part of a post operative respiratory exercise program, and more particularly to electronic devices for performing such measurements.
2. Prior Art
The use of incentive spirometers to encourage the post operative patient to fill his lungs completely has been proven to reduce the incidence of respiratory complications following surgery.
The incentive spirometers presently available fall into two categories, disposable and permanent with disposable elements. The disposable units are left with the patient during the course of his stay in the hospital and he is encouraged to inhale on it to fully inflate his lungs and gradually regain his preoperative lung capacity. A typical patient will be told to inhale deeply ten times an hour and with gradually increasing inspired volumes and flow rates until his performance matches at least his preoperative performance.
The permanent or reusable units, normally costing several hundreds of dollars each, incorporate a disposable element which may be a flow sensor or a volume canister and are used with a single patient at a time. When treatment is provided to a patient, the permanent part is provided with a new disposable element for each individual patient's use. Thus, one limitation of presently available permanent devices is that they either must be left with a single patient for his use throughout the day, thereby requiring a hospital to maintain a large inventory of expensive devices, or the devices must be moved from patient to patient thereby depriving the patient of the device until his turn comes again.
Spirometers may be constructed somewhat similar to the spirometers disclosed in U.S. Pat. Nos. 4,114,607 and 4,114,608.
The preferred embodiment of the present invention is particularly intended to operate in conjunction with the incentive spirometer which is the subject of U.S. Patent Application Ser. No. 739,271 filed Nov. 5, 1976.
These spirometers provide a mechanism to direct a patient to inhale air through a passageway having a flow regulator. Inhalation at a preset flow rate causes a visible indicator, such as a ball to rise to the top of a tube. A therapist may set up a program of respiratory exercise which calls for the patient to raise the ball to the top of the tube and hold it there for a specified time. The air flow regulator can be set to require various minimum flow rates for raising the ball to the top. The patient may be required to achieve the specified flow rate and hold the ball at the top of the tube for a specified time, a number of times per day. This type of program guarantees a certain minimum respiratory exercise.
In order to use these devices it is necessary for the patient, or therapist, to keep records by means of a pencil and paper and a stopwatch. Notations are made of the number of attempts made by the patient to achieve the required flow rate for the specified time, and of the number of successful attempts. To determine the volume of air inhaled on a particular attempt, the duration of time for which the ball remains at the top of the tube must be measured, e.g., by a stopwatch. Knowing the flow rate for which the regulator valve is set and the measured time, reference may then be made to charts to determine the volume of air inhaled, or the flow rate in cubic centimeters per second may be multiplied by the time in seconds; e.g., by hand.
The use of such devices is somewhat inconvenient in that either the patient must be supplied with a stopwatch and keep his own records, or a therapist must be present to time and make records whenever the patient performs an attempt to raise the ball.
The presence of a therapist may also be required to insure that the spirometer is being properly used. For example, if a patient is lying in bed and using the spirometer he may place the spirometer on blankets or on his stomach. Most likely the spirometer will not be truly vertical. The most valid measurements of air flow are made when the spirometer is vertical. The further from vertical the less accurate are the measurements of effort required to raise the ball.
Various devices designed to measure flow rate of a medium are known to applicant, including: Le Maitre et al, U.S. Pat. Nos. 4,078,554; Hutchinson, 2,333,791; Cooper, 3,754,546; Sanctuary et al, 3,818,901; and Kozak et al, 3,922,525.
Le Maitre shows a fairly complex spirometric device adapted for connection to the exhalation branch of a respiratory piping system. The device is particularly applicable to controlled delivery repsirators and uses a pressure pickup to provide data used in calculating the exhaled volume of air. The device is directed more at monitoring artificial respiration of a patient rather than controlling a post operative lung exercise program. Thus, Le Maitre makes use of the measured minimum and maximum pressures and Boyle's law rather than detecting the presence of an indicator.
Hutchinson shows a photoelectric device for counting globules of liquid of a known size and converting the number of such globules passing through a given point to a flow rate of the liquid.
Cooper provides an incentive spirometer of the type discussed earlier where there is only an indication given that a certain minimum flow rate has been achieved. In Cooper this is indicated by the turning on of the light. No measurement of the total volume of air inhaled is provided.
Sanctuary et al show a rather complex circuit arrangement for analyzing expired respiratory gases and measuring them. The volume of expired air is digitally displayed by means of a rotating slotted disc assembly.
Kozak shows a bidirectional spirometer with a moving vane type air flow sensor, the revolutions of the vane being counted to provide a measure of air flow.
It is an object of the present invention to provide a means for measuring and monitoring a patient's post operative respiratory exercise which does not require the use of a stopwatch, reference to charts, or hand calculations to determine the volume of air inspired.
It is another object of the invention to provide such a means which can be operated by the patient without requiring the presence of another person such as a therapist to assist in the patient's exercise program.
It is still a further object of the present invention to provide a means for calculating the volume of air inspired by a patient and for determining whether the patient was successful in his attempt to inspire a volume equal to or greater than that called for by the exercise program determined by the therapist.
It is again an object of the present invention to provide a means for recording the number of times a patient successfully inspires a volume of air equal to or greater than that called for by the exercise program and for determining whether the number of such successful efforts is equal to the number of successful efforts required by the exercise program.
Another object of this invention is to indicate to the patient the length of time he is required to hold his breath after he has successfully inspired the required volume of air.
A further objective is to provide a device which will automatically sense that its angular displacement from the vertical exceeds a preset value and in that event inhibit operation of the device.
The device should further display, on demand, the largest inhalation volume in the current series of inhalations.
It is an object of the present invention to provide such a device as discussed above which is portable and capable of operating in conjunction with a separate and independently operable spirometer such that the present device may be taken from the patient without depriving the patient of his spirometer.